The older main gun for small vessels. Equipped as the standard weapon on old destroyers. Both loading and rotation were hand-operated, but with its simple construction and low cost, it served for a long time as the main weapon of destroyers and escorts. Not intended for anti-air firing.

Category Equipment that consume 12cm Single Gun Mount during improvement not found

This gun's basic structure is based on British QF 4.7in. Mk.IV gun, which later produced domestically in Japan, which was used by old Japanese Destroyers (Up to the Mutsuki-class) as their primary armament.

The barrel of this gun was later mounted to high-angle and served as AA weaponry for early Japanese heavy cruisers (ie. Furutaka-class to Takao-class). Both classes had their AA guns changed for 12.7cm twin afterward, but Choukai alone was equipped with a 12cm single throughout her career).